Cantilever gates

    Cantilever gates

Benefits of cantilever gates and the calculation of forces

Author  ;   Huw Jones

Are cantilever gates worth it?

Cantilever gates are sliding gates without the ground track. The gate appears to hover across an opening like a wardrobe door.

There is a wow factor loved by residential clients, but some crucial advantages in not disturbing the roadway.

The technology has allowed creative designers to draw some impressive avant-garde gates, but they are not easy to provide safety for, necessary for gates with public access.

Any system that is practical and unique will find a market despite the increased cost.

The case for cantilever

Roadway. The advantage is being independant of the ground it crosses, so are ideal for sloping drives, rough surfaces, or roads used by heavy or tracked vehicles. The major work is done to one site of the opening, so traffic does not need to be disrupted for long.

Bearings are protected inside their track, so remain dry and lubricated, keeping maintenance low. There is no threat from debris like "the wrong sort of leaves" on the tracks. A balanced gate slides with has much lower rolling resistance.  Automation is lighter and safer, but gates are heavier so have a higher kinetic energy to decelerate. Bearings need to be rated 3-4 times higher than a sliding gate, coping with positive and negative vertical forces.

Cost and space. Gates are often 50% longer than the opening, so need a longer run back area. Bigger gates are more expensive in materials, transport, and lifting.

Vulnerability. Without the wheel's latteral support, these gates are vulnerable to side force damage when the gate is part opened. That includes wind loading on an infilled gate. The bearings give little side force protection.

Groundworks need to be heavier because of the increased forces, but they are shorter than the opening and don't need to be pretty. Once the concrete base is set, the gate bearings only need to be bolted into place and finely adjusted for ride height. An automated gate will still need a cable duct across the opening, so the roadway may need to be disturbed after all. 

Cantilever force calculation

The gate is shown in the position of highest force on bearing 1. When the gate is at the other end,  a slightly lower force will be on bearing 2.

F1 must not exceed 600kg for model 4, or 1000kg for model 7 

F1     =   Weight on bearing

Wf    =   Weight of front half

Wb   =   Weight of back half

Wt   =   Total weight of gate

G      =   Between bearings

Lo     =   Opening width

Lt     =   Total length of gate

Lg     =   Centre of gravity for Wb

Method 1

F1 = Wt + G (Wf Lo/2 - Wb Lg)

Method 1 calculates the F2 force from the torque difference between the front half of the gate and the back half. This method is correct. It assumes the gate density (kg/m) is the same across the opening. The separate value for Lg allows for an asymetric gate.

Method 2

F1 = Wt + Wt (Lo - Lt/2) / (Lt - Lo)

Method 2 is a simpler calculation for simple cases, but is good enough for non-critical applications. It assumes the gate density (kg/m) is the same for the front half as the back half of the gate, and that G is right on the end of the gate.

Conclusions

Cantilever running gear is the go to choice for industrial gate applications. They suit sites of high or heavy traffic like goods yards, bus depots, railway yards and building sites. Building sites on rough ground can site a temporary gate to comply with site safety.

Domestic applications are more difficult to justify, but find application where sloping drive make swing gates dangerous. There is undoubtedly a wow factor for a hovering gate that residential customers crave.